The present invention relates to a clamping element and a fuel injection system.
A clamping element in the form of a hold-down element is referred to in Japanese Published Patent Application No. 08-312503. The hold-down element holds down a fuel injector against a relatively high combustion pressure prevailing in the combustion chamber of the internal combustion engine. The hold-down element engages with a collar of the fuel injector at two circumferentially opposite locations, the collar resting with its lower side on the upper side of the cylinder head, so that the fuel injector is held down. The hold-down element is pulled on to the cylinder head by a clamping screw.
It is believed that the hold-down element referred to in Japanese Published Patent Application No. 08-312503 has the disadvantage that it is difficult to access the clamping screw if a fuel distribution line has already been fitted. If the fuel distribution line is not fitted until after the hold-down elements have been fitted and after they have been pre-tensioned to the defined retention force, the fuel injectors may no longer be moved or may only be moved if considerable force is applied, and tolerances at the connection points to the fuel distribution line, which in the case of high-pressure injection systems is rigid, may not be modified. Furthermore, a tight connection may only be achieved with difficulty or not at all. If the clamping screws are not tightened until after the fuel distribution line has been fitted, it may be difficult to access the clamping screws.
Furthermore, a hold-down device embodied as a clamp bracket similar hold-down element referred to in Japanese Published Patent Application No. 08-312503, is referred to in German Published Patent Application No. 197 35 665. In the case of the hold-down device, the cylinder head has a recess in which the collar of the fuel injector is arranged, so that the collar of the fuel injector on which the hold-down device acts is lowered into the cylinder head. It is believed that this has the disadvantages already mentioned.
A clamping element that holds a fuel injector in a mounting hole of a cylinder head of an internal combustion engine and rests against a fuel distribution line, is referred to in German Published Patent Application No. 197 56 102. The clamping element includes a spiral spring that extends between a spring holding element of the fuel injector and a spring holding element of the fuel distribution line. Furthermore, from German Published Patent Application No. 197 56 102, for assembly, one or more assembly clamps, which pre-tension the fuel injector, the fuel distribution line and the spiral springs and hold them in their position until assembly has been completed, should be provided.
It is believed that a disadvantage of the clamping element referred to in German Published Patent Application No. 197 56 102 is that with a spiral spring it may be difficult to achieve the necessary high clamping forces. Furthermore, it may be disadvantageous that, if a pre-mounted unit that includes a fuel distribution line, clamping elements and fuel injectors is fitted, additional assembly clamps may be required. Moreover, it may be disadvantageous that, when the fuel distribution line is fitted all spiral springs should be tensioned simultaneously and adjustments of individual fuel injectors to any tolerances in the mounting hole in question may not be carried out consecutively.
By contrast, it is believed that an exemplary clamping element according to the present invention has the advantage that high clamping forces may be achieved using small clamping element dimensions.
It is believed to be advantageous if the first step ring and the second step ring have coaxial holes into which the fuel injector and a connection piece of a fuel distribution line may be inserted. Thus, small design dimensions and a favorable arrangement of the clamping element may be achieved because only one circumferential collar around the fuel injector is required to bear the clamping force. Furthermore, it is believed to be advantageous that the clamping element may be held in the holes.
It is believed to be advantageous if the first step ring and the second step ring are held so that they are concentric relative to one another by shoulder of the first step ring or second step ring that engages with a corresponding step of an axial hole of the other step ring. As a result, the clamping element may be a compact, self-contained component, which may be inserted as a single element during assembly.
It is believed to be advantageous if the first step ring and the second step ring each have on their circumference a bolt that is rotatably mounted axially parallel to the step ring and is axially movable, and have a hole that extends across it, and if the hole of one bolt is a threaded hole, and if a screw that is held in the hole of the other bolt is present and engages with the threaded hole. Thus, the first and second step ring may be rotated against one another and the clamping force of the clamping element may be adjusted. For example, the screw may be arranged so that it is easily accessible, as the axis of the screw points away from a plane that is at least approximately formed by the fuel injectors and the fuel distribution line and does not lie in that plane.
It is believed that an exemplary fuel injection system according to the present invention has the advantage relative to the related art that the retention force is imparted against the fuel distribution line. As a result, no additional components may be required, which may save space. Moreover, the sequence of tensioning may be chosen freely.